Heat exchanger

ABSTRACT

A compact heat exchanger and/or fluid mixing means comprises a bonded stack of plates, the stack comprising at least one group of plates, the group comprising one or more perforated plates ( 10 ) sandwiched between a pair of primary separator plates ( 40, 62, 64 ), characterised in that each perforated plate ( 10 ) has perforations ( 14 ) arranged in rows across the plate in a first direction, with a land ( 16 ) between each adjacent pair of perforations ( 14 ) in a row and with ribs ( 18 ) between adjacent rows, the lands ( 16 ) forming barriers to flow in a first direction across the plate and the ribs ( 18 ) forming barriers to flow in a second direction across the plate, the second direction being normal to the first direction, the ribs ( 18 ) having vents ( 20 ) through a portion of their thickness, the vents ( 20 ) extending from one side of a rib ( 18 ) to the other side in the second direction, whereby flow channels are provided through the vents ( 20 ) and the flow channels lying between each adjacent pair of lands ( 16 ) provide a flow passage to cross the plates in the second direction, the passageways in the group of plates being separated from passageways in any adjacent group of plates by one of the separator plates ( 40 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/937,666 filed on Sep. 26, 2001 which in turn claims priority toforeign applications for patent, Great Britain Serial No. 9907032.8,filed Mar. 27, 1999, Great Britain Serial No. 9914364.6, filed Jun. 19,1999, and international patent application serial number PCT/GB00/00631filed on Feb. 24, 2000 which are hereby incorporated by reference.

BACKGROUND OF INVENTION

This invention relates to a compact heat exchanger and/or fluid mixingmeans which incorporates a series of plates having apertures whichdefine a plurality of passages through which fluid may flow.

Compact heat exchangers are characterised by their high “area density”which means that they have a high ratio of heat transfer surface to heatexchanger volume. Area density is typically greater than 300 m²/m³ . andmay be more than 700 m²/m³. Such heat exchangers are typically used tocool (or heat) process fluids.

One well known but expensive to manufacture type of heat exchanger isthe so-called tube and shell heat exchanger. Essentially such heatexchangers consist of an exterior tubular shell through which run anumber of longitudinally-extending smaller diameter tubes carrying oneor more fluids. Other fluids, with which heat is to be exchanged,typically pass transversely across the heat exchanger such that heat isexchanged through the tube walls. A large number of tubes may be neededand they each have to be individually and accurately fixed/secured intoa header plate at each end of the shell. In each case holes need to bedrilled in the header plates very accurately to locate the tubes. Highquality tested tubing then needs to be assembled into the plates andbrazed or welded or mechanically-expanded into position. As the tubesare reduced in diameter to increase surfaces available for heat transferand hence performance/compactness, the more difficult and expensive suchconfigurations become to manufacture.

A second known type of heat exchanger is the so-called primaryplate/secondary plate type exchanger in which a stack of plates isassembled, the stack having primary plates which directly separate twodifferent fluid streams and secondary plates between adjacent primaryplates. The secondary plates act as fins which add to the strength ofstructure and may be provided with perforations to provide additionalflow paths for the fluids. The plates are usually bonded together bybrazing but this may have the disadvantage of affecting the physicalproperties of the plates in the brazed regions—or may introduce into thesystem, by means of the braze material, a potentially less satisfactorystructure in terms of strength and corrosion resistance. It has beenproposed to bond the plates together by diffusion bonding but asatisfactory construction that can withstand the high pressures involvedhas not been achieved and the fins may buckle during the bondingprocess.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedconstruction of this second type of heat exchanger which can besatisfactorily made by, for example, diffusion bonding or by brazing. Italso aims to provide a heat exchanger construction which can also bereadily adapted for use as a fluid mixing means, e.g. it can be used asa chemical reactor in which fluids which are to react together aremixed. Thus, where a reaction is exothermic, the invention may provide ameans whereby the exothermic heat of reaction may be removed efficientlyor, alternatively, it may be used to supply heat to an endothermicreaction. The products of the invention are also useful as fuelreformers and gas clean-up units associated with fuel cell technology.

Accordingly the present invention provides a heat exchanger or fluidmixing means comprising a bonded stack of plates, the stack comprisingat least one group of plates, the group comprising one or moreperforated plates sandwiched between a pair of primary separator plates,each perforated plate having perforations arranged in rows across theplate in a first direction, with a land between each adjacent pair ofperforations in a row and with ribs between adjacent rows, the landsforming barriers to flow in the first direction across the plate and theribs forming barriers to flow in a second direction across the plate,the second direction being normal to the first direction, the ribshaving vents through a portion of their thickness, the vents extendingfrom one side of a rib to the other side in the second direction,whereby flow channels are provided through the vents and the flowchannels lying between each adjacent pair of lands provide a flowpassageway to cross the plates in the second direction, the passagewaysin the group of plates being separated from passageways in any adjacentgroup of plates by one of the separator plates.

Although the group of plates may in fact contain only one perforatedplate, there may be two or more perforated plates in the group of platesand in this embodiment adjacent perforated plates are aligned wherebythe perforations of a row in one plate lie in correspondence with thoseof adjacent plates so that the lands and ribs of the plates lie incorrespondence respectively with each other.

The invention will be more particularly described below with referenceto embodiments in which the, or each, group of plates contains two ormore perforated plates.

It will be appreciated that the flow passages can equally be provided inthe first direction instead of the second direction, i.e. the lands areeffectively the ribs containing the vents and the ribs are the lands.

The separator plates may be unperforated to provide complete separationof the passageways of the respective groups of plates. Alternatively,the separator plates may contain holes positioned and sized to providecontrolled mixing of the fluids in those passageways. Such a separatorplate will be referred to below as a mixing plate.

As indicated above each group of perforated plates preferably comprisesat least two perforated plates but may contain three or more adjacentperforated plates as desired. A stack may, for example, comprise two ormore groups of perforated plates separated by separator plates, eachgroup containing two perforated plates having their perforations alignedin rows.

The passageways across the plates preferably traverse across the platesonce only from a first edge to a second edge. However, in an alternativefirst specific embodiment, the passageways at one or both plate edgesmay be turned, e.g. by an appropriate passageway arrangement, through anangle whereby the passageway defined by the channels continues in adifferent direction through the stack, e.g. in the opposite direction soas to return from the second edge to the first edge.

In a second specific embodiment two or more separate passageways areprovided across a group of plates whereby streams of different fluidsmay flow parallel to each other in the same layer provided by said groupof plates. This embodiment can provide improved temperature profilesacross the plates and reduced thermal stress.

Because the plates are stacked with the perforated plates of each groupaligned with their perforations in rows, it will be appreciated that thesolid regions (i.e. ribs and lands) of those plates between the rows ofperforations and between the perforations are also aligned in rows. Asthe perforated plates, therefore, are stacked one above each other, theribs and the lands are aligned through the stack and this providesstrength through the assembled stack whereby the pressures generated inthe bonding process can be withstood. The invention, therefore, providesa stack structure that can be bonded without the risk of the fins of thesecondary plates collapsing under the pressures generated. The fins alsoprovide the means of withstanding internal pressures in the operatingstreams. The rows of ribs and of lands may run in parallel lines acrossthe plates but this is not essential.

The perforations may be of any desired shape but are preferablyelongated slots.

The plates may be rectangular, square or circular for example or of anyother preferred shape.

Where the plates are square or rectangular, each row of slots may extendfrom a first edge of the plate parallel to a second edge of the plateand for substantially the whole length of that second edge. It will beappreciated that a substantially unperforated edge or border willnormally be required around the perimeter of the major faces of theplate to enable the plates of the stack to be bonded together and toprovide pressure containment for the stream or streams. However, acompletely unperforated border is not essential and slots in the bordermay be required for inlet and outlet means, for example. A plurality ofrows of slots may, therefore, extend across the plate from the firstedge to the opposite, third, edge.

Where the plates are circular the rows and passageways may extend fromthe outer perimeter as a segment of the circle towards the centre.

In one particular arrangement of the aforesaid second embodiment, astack may be built up of one or more similar groups of plates, eachgroup comprising an upper and a lower unperforated separator plate, amultipassageway input layer in contact with one separator plate and acorresponding multi-passageway output layer in contact with the otherseparator plate, a centrally-disposed layer having at least onepassageway for a first fluid and two or more transfer passageways for afluid from each passageway of the input layer, a first auxiliaryperforated plate lying between the input layer and thecentrally-disposed layer and a second auxiliary perforated plate lyingbetween the output layer and the centrally-disposed layer, theperforations in the first auxiliary perforated plate being positioned totransfer fluid from each passageway of the input layer to thecorresponding transfer passageways in the centrally-disposed layer andthe perforations in the second auxiliary perforated plate beingpositioned to transfer fluid from the transfer passageways to thecorresponding passageways of the output layer. The centrally-disposedlayer can conveniently be formed of a plurality of main perforatedplates as described above, as can the input and output layers.

The perforations or slots are preferably photochemically etched throughthe plates by known means, although spark erosion, punching or any othersuitable means may be used, if desired.

The vents may be similarly formed and are preferably formed byphotochemical etching. The vents are conveniently formed in the ribs onone surface of the plate so as to extend partially into the thickness ofthe rib (i.e. the thickness of the plate.). They may for example be of adepth equal to about one half of the plate. However, it may beadvantageous to form vents in both surfaces of the plate, in which casethe vents in one surface should preferably be staggered from those inthe other surface.

For convenience the invention will hereafter be described with morespecific reference to vents in the ribs although it will be appreciated,as indicated above, that they may equally be formed in the lands ratherthan the ribs.

A stack of adjacent perforated plates has rows of lands and rows ofribs. In the ribs between any adjacent pair of rows of lands there willbe a plurality of vents forming flow channels across the plates. Theseflow channels together form a flow passageway that is separated fromadjacent groups of flow channels, i.e. adjacent flow passageways, by therows of lands. Thus each of the plurality of fluid channels forming anindividual passageway may pass through the stack without anycommunication with the channels of another passageway. No mixing offluid in those passageways can, therefore, take place and the stackfunctions purely as a heat exchanger with fluids at differenttemperatures passing through different groups of perforated plates orpassing through different passageways in the same group of perforatedplates.

In another embodiment of the invention there is providedintercommunication at selected positions between adjacent passageways.Thus cross-channels or cross vents may be etched or otherwise formed inthe lands of the plates to provide access between adjacent passageways.The cross vents may be formed at any desired position along thepassageways. Thus fluid flowing through separate passageways may beblended at prearranged positions on its journey through the passagewaysthrough the stack and this blending may be employed to ensure good fluiddistribution and to improve heat exchange capability. (It will beappreciated that where the vents are in the lands rather than the ribs,then the cross vents will be in the ribs rather than the lands.).

Alternatively or additionally, inlets for a further fluid may beprovided through the peripheral borders of the plates. Thus reactant maybe introduced and mixed via the peripheral border inlets whereby thestack may be employed as a chemical reactor.

In another embodiment the invention provides a stack in which a fluidstream from one group of perforated plates may be injected into a fluidstream in an adjacent group of perforated plates. Injection holes forthis purpose are provided in a mixing plate which separates the twogroups of perforated plates. So-called “process intensification” can beachieved by this means, and any reaction caused by the injection of afirst fluid into a second fluid can be controlled by the pressuredifferential between the two streams, the size, numbers and spacing ofthe injection holes and by sandwiching the second stream between thefirst stream and a coolant or heating stream, as appropriate.

The density of the slots, and hence of the ribs or fins between each rowof slots, may be varied, as required. Thus the number of slots per unitwidth or per unit length of a plate may be arranged to suit anyparticular flow/pressure drop/distribution change requirements.

The vents in adjacent pairs of ribs are preferably offset from eachother so that fluid flow across the plates is continually changingdirection in that it must follow a sinuous route. It will be appreciatedthat each time the flow passes through a vent, the flow area and hencevelocity changes resulting in turbulence and good heat transfer throughthe mass of the plates, albeit with associated pressure drops. Theskilled man of the art will, therefore, be able to design a wide varietyof heat exchanger characteristics and to optimise the desired effects.

The vents may be formed normal to the direction of the rib or they maybe angled through the rib so as to provide an increased sidewayscomponent of movement. The vents may be tapered, especially narrowed inthe direction of flow to their exit into a slot. Thus flow velocity willincrease as fluid enters a vent from a slot and will increase furtherdue to the tapering effect.

It will also be appreciated that the main flow direction across theplates is through the vents and that flow normal to that direction, i.e.through any cross vents that are provided, will normally be restrictedby the provision of fewer and/or smaller cross vents.

The rows of slots may extend linearly across the plate but this is notessential and they may be arranged in other desired patterns, e.g.herringbone or chevron.

The plates may be provided at their edges with extensions, e.g. in theform of lugs to assist location of the plates in a stack. Such lugs maybe designed to be broken off after the stack has been assembled, e.g. byetching partway through their thickness along a line where the lug joinsthe plate. Alternatively the extensions may fit together in the stack toprovide, e.g. one or more tanks on the side faces of the stack. Eachextension may, for example, be in the form of a flat loop, e.g. ofsemi-circular profile, providing an aperture at the edge of the plate,the apertures of adjacent plates forming the volume of the tank when theplates are stacked together. The loops may be attached to the plate notonly at their ends but also across the aperture by means of narrowligaments. The tanks so formed can each feed fluid, e.g. process fluid,coolant or reactant which is fed into the tanks, into the channels ofone passageway. Thus a tank will be coterminous on the side of the stackwith the height and width of the passageway, i.e. a group of channels,to be fed. Where the stacks are polygonal in plan, a tank may beprovided on one or more of the side faces of the stack. Where the stacksare circular in plan, a number of tanks may be spaced around theperimeter as desired.

Plates used to form the products of the invention may also be providedwith a hole, e.g. disposed centrally through each plate, whereby a stackof the plates has a centrally-disposed discrete passageway for a fluidstream through the stack. To compensate for the loss of flow area wheresuch a central hole is provided, it is possible, where the plate isprovided with integral tank loops, to extend the plate outwardly betweenadjacent loops.

The plates of a stack are preferably of the same material and arepreferably thin sheets of metal, e.g. of 0.5 mm thickness or less. Thematerial is preferably stainless steel but other metals, e.g. aluminium,copper or titanium or alloys thereof, may be used.

Inlet and outlet headers or manifolds for the different fluids may besecured to the stack after bonding together of the stack plates or,alternatively, may be formed from integral features on the plates.

As indicated above, the components of a stack may be bonded together bydiffusion bonding or by brazing. Diffusion bonding, where possible, maybe preferred but, in the case of aluminium, which is difficult todiffusion bond, brazing may be necessary. It is then preferable to cladthe aluminium surfaces, e.g. by hot-roll pressure bonding, with asuitable brazing alloy, in order to achieve satisfactory bonding by thebrazing technique, although other means to provide the braze medium maybe used, e.g. foil or vapour deposition.

The invention is particularly useful where it is desired to build up alarge heat exchanger by bonding side by side a number of heat exchangerunits. Each unit can be provided by a stack of plates of the invention.Each stack may, for illustration purposes only, be formed of plates of,say, 300 mm width by 1200 mm length and of the desired height dependingon the thickness and number of plates. Several stacks can be placed sideby side on a separator plate and then the assembly closed at the top byanother separator plate. If six stacks, for example, are utilised sideby side, a heat exchanger of about 1800 mm flow length is achieved. Allrequired lugs, mitre sections, spacers, etc. can be formed integrallyand built up from appropriate formations on each plate and all thestacks will be of the same height, being made up of identical plates.Such an arrangement has significant advantages in the manufacture of,for example, “cryogenic” aluminium heat exchangers, which conventionallyhave to be built up of layers of corrugations with separate side bars.Unless the height of the side bars relative to the height of thecorrugations is correct lack of uniformity and unsatisfactory brazing ofthe product may result.

It is known that chemical reactions can be catalysed inside a structuresuch as a heat exchanger by providing a deposit of catalytic material inthe internal passageways through which the fluid(s) to be catalysed arepassed.

The perforated plates used in the present invention are particularlyuseful in this respect as the surfaces of the ribs, lands and vents canreceive a catalytic material coating of relatively modest thickness andthe slots in the perforated plate can receive a much thicker deposit ofthe catalytic material. Thus, for example, where the vents extend intothe thickness of the ribs to a depth equal to about one half of theplate thickness, the catalyst deposit in the slots can be of depth up tohalf the plate thickness without causing any blockage of the vents.

In a further embodiment of the invention is provided a heatexchanger/catalytic reactor having a plurality of passageways to containcatalytic material to promote a chemical reaction in fluid(s) to bepassed through those passageways, those passageways being separated byan intervening plate from a stack of one or more parallel perforatedplates having a vented rib structure according to the present invention.Thus the stack of plates separated by the intervening plate from theadjacent passageways, which later will be filled with catalyticmaterial, is formed from perforated plates, each having perforationsarranged in rows across the plate in a first direction, with a landbetween each adjacent pair of perforations in a row and with ribsbetween adjacent rows, the lands forming barriers to flow in the firstdirection across the plate and the ribs forming barriers to flow in asecond direction across the plate, the second direction being normal tothe first direction', the ribs having vents through a portion of theirthickness, the vents extending from one side of a rib to the other sidein the second direction, whereby flow channels are provided through thevents and the flow channels lying between each adjacent pair of landsprovide a flow passage to cross the plates in the second direction.

Once the heat exchanger structure has been completed and tested, thecatalytic material may be packed into its passageways. However, thepacking of the catalytic material will normally be completed immediatelyprior to the installation of the heat exchanger/reactor into its desireduse position.

The passageways to contain the catalytic material are preferably definedbetween parallel ribs running the length of their plates to allowconvenient introduction of the catalytic material and its subsequentremoval at the end of its life cycle. The passageways may be closed offat one or both ends by a mesh to retain the catalytic material.

By means of this further embodiment, heating or cooling can veryeffectively be provided for the chemical reaction by passing a heatingor cooling fluid through the stack of plates adjacent to the layerscontaining the catalyst. As indicated above, this structure causes suchtortuous flow and turbulence that very good heat transfer properties canbe achieved, especially with gaseous fluids. The catalysed reaction may,therefore, if exothermic, be effectively cooled by passage of a suitablecooling fluid, or if endothermic, may be heated and hence initiated orimproved by passage of a suitable heating fluid, through the stack.

This further embodiment may also be used in conjunction with theabove-described injection construction, i.e. the heat exchanger may havea first stack containing the passageways containing catalytic material,an adjacent second stack separated from the first stack by anintervening plate with injection holes and a third stack of the coolingor heating construction. The first stack may, for example, lie betweenthe second and third stacks, or they may lie in the order—first, second,third. Needless to say, these three stacks maybe repeated a number oftimes to form the complete heat exchanger/reactor.

Embodiments of the invention will now be described by way of exampleonly with reference to the accompanying drawings in which:

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a plan view of one slotted plate for use in the invention;

FIG. 2 is a plan view in enlarged scale of a portion of a stack ofplates of the type shown in FIG. 1;

FIG. 3 is an plan view of a portion of another plate for use in theinvention showing the staggering of vents;

FIG. 4 is a vertical section through a portion of one stack of plates ofthe invention;

FIG. 5 is a similar view to FIG. 4 of a portion of another stack ofplates of the invention;

FIG. 6A is a plan view of an unperforated intervening plate, i.e. aseparator plate;

FIG. 6B is a plan view of a perforated intervening plate, i.e. a mixingplate;

FIG. 7 is a diagrammatic plan view of a modified slotted plate of theinvention;

FIG. 8 is a section along line VIII—VIII of FIG. 7;

FIG. 9 is a perspective view, partly exploded, of a heat exchanger ofthe invention suitable for use as a catalytic reactor;

FIG. 10 is a diagrammatic representation of the plate arrangement in theheat exchanger of FIG. 9;

FIG. 11 is a plan of a stack of three plates used in the heat exchangerof FIG. 9 to provide the passageways for a process fluid to undergo achemical reaction;

FIG. 12 is a section on line XII—XII of FIG. 10;

FIG. 13 is a plan view of a stack of plates used in the heat exchangerof FIG. 9 to provide reactant fluid to be injected into the processfluid;

FIG. 14 is a plan view of another stack of plates similar to the platesof FIG. 13, which stack is used in the heat exchanger of FIG. 9 toprovide a cooling or heating fluid as required;

FIG. 15 is a plan view of a separator or intervening plate to liebetween the stacks of FIGS. 13 and 14; and

FIG. 16 is a plan view of an injection plate to lie between the stacksof FIGS. 11 and 13.

DETAILED DESCRIPTION OF PREFERRED AND ALTERNATE EMBODIMENTS

In FIG. 1 a rectangular plate 10 for use in the invention has a pair ofintegral side bars 12A and 12B opposed across two sides of the plate.

Between side bars 12 and 12B extend a plurality of parallel rows ofslots 14, each slot extending entirely through the thickness of theplate and being separated from an adjacent slot in the same row by aland 16. Lands 16 extend continuously across the plate in rows parallelto side bars 12A and 12B. Each slot is separated from an adjacent slotin the next row of slots by a rib 18. Ribs 18 extend in parallel rowsacross the plate between side bars 12A and 12B.

Each rib 18 is etched to have at least two vents 20 between each pair oflands 16 or between a land 16 and a side bar 12A or 12B. The ventsextend partway through the rib thickness, i.e. into the plane of thepaper, and provide communication, i.e. flow channels, between a slot inone row and an adjacent slot in the next row of slots. (Vents are onlyshown in one corner region of plate 10 for convenience but it will beappreciated that they are formed across the whole of the plate betweenthe side bars.). The vents are shown and described in more detail withreference to FIGS. 2 to 6 below. The vents 20 enable the main flowpassageways for a fluid passing across the plate, when stacked with oneor more identical plates, to be in the direction shown by the arrows A.As the vents in adjacent ribs are staggered, the fluid passagewaysextending across the plate, between adjacent parallel lands 16 aretortuous.

The lands 16 are also provide with cross vents 22, again partway throughtheir thickness, to provide cross-flow channels between adjacentpassageways. Again this adds to the turbulence and heat transferproperties. It will be noted that this cross-flow, indicated by arrow B,is through fewer spaced vents so that the main thrust of the flowremains in the general direction indicated by arrow A. It will also benoted that the cross vents are staggered with respect to side vents inadjacent lands.

In FIG. 2 is shown a stack of four plates 30A, B, C, D, each similar tothe type shown in FIG. 1. Each plate has rows of slots extending betweenparallel ribs 38A, B, C, D, adjacent slots being separated by lands 36A,B, C, D. The slots of each plate stack with the slots of the three otherplates to form large slots 34.

An unperforated boundary plate 40 lies in contact with lowermost slottedplate 30A. Similarly another unperforated plate can lie in contact withuppermost slotted plate 30D whereby fluid passing across plates 30A to30D is confined between the unperforated plates.

Ribs 38A, B, C, D each have vents 32 etched partway through theirthickness and providing channels for fluid flow between a slot 34 on oneside of the rib and another slot 34 on the other side of the rib. Thesevents thereby provide fluid flow passageways across the plates in thegeneral direction of arrows A. As can be seen, the flow can besinusoidal, from side to side and up and down owing to the staggerednature and the different height of the vents 32.

Lands 36A, B, C, D are provided with cross vents 33, which are fewer innumber than vents 32, but provide flow through the lands in thedirection of arrows B.

The effect of the staggering of the vents is shown more clearly in FIG.3. Here a plate 50 has slots 52 between ribs 54. Each rib 54 has aplurality of vents 56 etched through its thickness to provide a seriesof rib blocks 54A, the vents providing flow channels between adjacentslots 52. Because the vents in one rib are staggered from those inadjacent ribs, fluid flow across the plate, as indicted by the arrows,is necessarily tortuous.

As indicated above, the plate may have a coating of catalyst on itssurfaces and the coating may form a thick deposit in slots 52 up to alevel with the base surface of coated vents 56. This can conveniently beachieved in the manufactured structure by passing the catalytic materialthrough the structure in known manner to achieve the deposits. Inparticular the structure may comprise single slotted plate layersbetween pairs of separator plates or pair of slotted plates one invertedon top of the other with their rib blocks 54A in contact, each pairlying between a pair of separator plates. In the latter instance, thecatalyst material may be passed through the structure to leave thedeposits in the slots of one plate and the structure then inverted toreceive more of the catalytic material, which will then deposit in theslots of the second plate of each pair of slotted plates.

In FIGS. 4 and 5 are shown two stacks of plates of the invention toillustrate possible variations in the siting of the vents.

In FIG. 4 are shown four identical slotted plates 60 stacked between apair of unperforated boundary plates 62, 64. Each plate 60 has vents 66etched into its face 60A and vents 68 etched into its opposite face 60B.Vents 66 and vents 68 are staggered from each other along the rib of theplate.

Regions 70 of each plate indicate a land and it will be appreciated thatthis pattern of vented ribs between adjacent lands is repeated acrossthe plate as indicated in FIG. 1 along its entire length.

In FIG. 5 the unperforated plates corresponding to plates 62 and 64 ofFIG. 4 have been removed. Again four slotted plates are stackedtogether. The plates, 72A, B, C and D, are identical but alternateplates have been turned over. Thus each plate has in its rib regionthree slots 74 on one face and two slots 76 on the other face. Plate 72Ahas its three slots 74 uppermost and its two slots 76 lowermost. Plate72B has its two slots 76 uppermost and in correspondence with the twoslots 76 of plate 72A. Its lowermost slots 74 are in correspondence withslots 74 of plate 72C. Similarly slots 76 of plate 72C, being lowermost,are in correspondence with the slots 76 of plate 72D. By this meanslarger vent channels are provided through the ribs.

FIG. 6A shows a single unperforated boundary plate TS that can be usedto separate the flow passageways through one group of main perforatedplates from the flow passageways of another group of main perforatedplates.

FIG. 6B shows a single boundary mixing plate TP. Plate TP has groups ofcircular holes TPP through its thickness, although it will beappreciated that holes of different shape, size and groupings may beused. When plate TP is used as a boundary plate between two groups ofmain perforated plates, a first fluid flow across one group at higherpressure than a second fluid flowing across the other group will beinjected into the second fluid at a controlled rate.

In FIGS. 7 and 8 is shown plate 80 having a series of square slots 82etched or otherwise formed through its thickness. Slots 82 extend inrows across the plate, eight rows being shown. Between adjacent slotsare channels provided by main vents 84 formed partway through thethickness of the plate and cross-channels provided by cross-vents 86also formed partway through the thickness of the plate.

The four rows of slots in the right hand half of the plate extend fromedge 80A to opposite edge 80C of the plate and are fed from an inlet Iat edge 80A, fluid being injected into the slots via edge vents 841. Thefluid can cross towards edge 80C via vents 84, with some of the fluidmoving to a different row of slots via the cross-vents 86.

Fluid flow is indicated generally by the arrows.

Fluid reaching the slots 82 nearest to edge 80C of the plate is forcedto use one or more cross vents 86 and thereby to cross over to one ofthe four rows of slots extending in the left hand half of the plate. Thefluid then travels back from edge 80C to edge 80A of the plate where itexits through outlet O formed by the edge vents 84′.

A second or further fluids may be injected into the fluid passing acrossthe plate by means of side injection vents 88, 90 and 92 in edges 80B,80C and 80D respectively of the plate.

It will be appreciated that these injection vents will be provided witha one-way valve or other e.g. pressure differential means, to preventfluid flowing across the plate from exiting through these vents.

The injection vents may be positioned to achieve the optimum performancefrom the injected fluids(s). It will be noted that each slot 82 adjacentan edge of the plate is provided either with an injection vent to the jedge of the plate or with a blind vent 94. These blind vents may bereadily converted to full vents so that a wide range of injectionpatterns is possible.

It will be appreciated that the vents and cross vents in FIG. 7 areshown in simplified form for clarity and that two or more vents may beprovided between each adjacent pair of slots and that thecross-sectional areas of the vents and their numbers may be variedacross the plate to achieve desired flow characteristics.

In FIG. 9 a heat exchanger/catalytic reactor 100 has an inlet 101 and anoutlet 102 for coolant (or if required a heating fluid to initiate anendothermic reaction) and an inlet 103 and an outlet 104 for a reactantfluid which is to be injected as described in greater detail below intoa process fluid which passes through the open-through passageways 105through reactor 100 in the direction of arrow A. The inlets and outletslead into and out of tanks 110 and 111 respectively from which thefluids are fed into their appropriate stacks.

Reactor 100 will of course be connected in a fluid-tight manner to apipeline (not shown) or other means of passing the process stream from asource, through the reactor 1000 to a suitable receiving vessel byconventional means. Such connection may conveniently be made by boltingflanges 100A and 100B at either end of reactor 100 to correspondingflanges provided in the pipeline or other means using bolt holes 100C.

The passageway or channels 105 are defined in stacks of plates to bedescribed with reference to FIGS. 11 and 12 below. These channels may bepacked with catalyst and, after a period of use, the reactor 100 may bereadily unbolted from its pipeline, the spent catalyst removed fromchannels 105 and fresh catalyst inserted so that the reactor is readyfor re-use.

A mesh 105A mounted in a frame 105B can be clamped to frame 100B and/or100A to retain the catalyst in the passageways 105.

The order or arrangement of the plates in the reactor 100 is shown inFIG. 10.

At each end of the total stack of plates is a solid unperforated plateS, which is described with reference to FIG. 15 below.

Above bottom plate S in FIG. 10 is a stack A of plates definingpassageways to receive the coolant (or heating) stream through inlet101. The plates of stack A are described with reference to FIG. 14below.

Above stack A is another solid unperforated separator plate S. Abovethat plate S is a stack of plates B defining passageways to receive areactant fluid. The plates of stack B are described with reference toFIG. 13 below.

Above stack B is an injection or mixing plate I, which is described withreference to FIG. 16 below.

Above injection plate I is a stack C of plates defining the passageways105 referred to above for the process fluid. The plates of stack C aredescribed below with reference to FIGS. 11 and 12.

Above stack C is another solid, unperforated separator plate S.

This structure may then be repeated with another stack A and so on asmany times as is required to build up heat exchanger/reactor 100 to thedesired capacity.

A separator plate is shown in FIG. 15. It has a rectangular plan formwhere border region 156 can be bonded to the corresponding borderregions of adjacent plates by one of the means discussed above. Borderregion 156 encloses and merges into an unperforated, i.e. solid, centralregion 157 which prevents fluid flow passing from one side of plate S toits other side. Adjacent each corner of the plate S is a loop extension158 defining an enclosed region or aperture 159. These loops 158 stacktogether with corresponding portions of the other plates stacked in theheat exchanger to form two inlet and two outlet tanks 110 and 111respectively, one of each being visible in FIG. 9.

The top plate of stack A is shown in FIG. 14. Two or more such plates170 are required and each is of a rectangular form having a borderregion 171 for bonding to adjacent plates and a central region 172.Region 172 is of vented rib construction—not shown here but, forexample, as shown in FIGS. 1 to 3. As with plate S, adjacent the cornersof plate 170 are loops, two of which, 173A and 173B, in oppositecorners, enclose an aperture 174 and the other two of which 173C, 173D,open into central region 172, thereby providing entry and exit forcoolant fluid passing across and through stack A via inlet 101 andoutlet 102 shown in FIG. 9.

The top plate of stack B is shown in FIG. 13. Two or more such plates180 are required and they are of identical structure to plates 170. Thusthey have a border region 181 enclosing a central pin-fin region 182.They have enclosed loops 183A and 183B and loops 183C and 183D, thelatter two loops providing an inlet and an outlet for reactant fluid topass across and through stack B via inlet 103 and outlet 104 of FIG. 9.

Injector plate I is shown in FIG. 16. It is of the same rectangular formas the plates described above. Its border region 191 can be bonded tothe border regions of adjacent plates and it encloses and merges into acentral region 192. Region 192 is not imperforate but has a series ofinjection holes 190 passing through its thickness. Thus reactant fluidpassing through stack B on one side of plate I can be arranged to be athigher pressure than process fluid passing through stack C on the otherside of plate I, whereby the reactant fluid will be injected throughholes 190 into the process fluid to cause the desired chemical reaction.Holes 190 can be of size and distribution to suit the required amount ofreactant fluid to be injected.

As with the previously described plates, plate I has corner loops 193A,B, C, D, and each loop encloses an aperture 194 to form part of thetanks 110 and 111 shown in FIG. 9.

The plates 120 of stack C are shown in FIGS. 11 and 12. Three plates areshown in this stack although it will be appreciated that more or lessplates may be used, as desired. Again, plates 120 are rectangular with aborder region 121 along their two longer edges. Border regions 121A,121B along their shorter edges are designed to be removed by cuttingalong lines XII—XII and XI—XI after the plates have been bonded to theother plates in the heat exchanger.

Central region 122 of each plate 120 has a series of parallel ribs 123running along its longer length. Between adjacent pairs of ribs 123 andbetween each outermost rib 123 and border region 121 lie open channels124, (equivalent to channels 105 in FIG. 9). The channels extendcompletely through the thickness of the plate. When ends 121A and 121Bare removed process fluid can pass from one side of stack C, where ends121B were, along channels 124 and out at the other end, i.e. where ends121A were, as indicated by arrows A. Arrows A here correspond to arrow Ain FIG. 9.

It will be appreciated that ribs 123 are held in their positionsinitially by being joined to ends 121A and 121B of plate 120. When theplates of the stacks are bonded together, ribs 123 bond to a plate Ibelow or plate S above (as in the arrangement shown in FIG. 10) or tothe corresponding ribs of adjacent plates 120. Thus when ends 121A and121B are removed, the ribs remain firmly in place.

Channels 124 may be packed with catalyst to promote the reaction betweenthe process fluid passing across and through stack A with the injectedreactant fluid for stack B.

If it is desired to equalise pressure between the catalyst channels 124,vents may be formed partway through the thickness of ribs 123. Moreover,all the channels 124 in a plate 120 need not be of the same width. Bythis means, different flow rates may be promoted in different channelsor poor uniformity of flow distribution through the channels may becompensated for by having wider channels at the edges of the plate.

Plates 122 each have corner loops 125A, B, C, D, completely enclosingapertures 126, to form part of the tanks 110 and 111.

By way of example only, plates 120 may be about 2 mm in thickness andthe requisite number of such plates will be stacked together to give thedesired channel height.

1. A heat exchanger or fluid mixing means comprising a bonded stack ofplates, the stack comprising at least one group of plates, comprisingone or more perforated plates (50) sandwiched between a pair of primaryseparator plates, each perforated plate has a plurality of perforationsarranged in rows across the plate in a first direction, with a landbetween each adjacent pair of perforations in a row and with ribs (54)between adjacent rows, the lands forming barriers to flow in the firstdirection across the plate and the ribs forming barriers to flow in asecond direction across the plate, the second direction being normal tothe first direction, the ribs (54) having vents (56) through a portionof their thickness, the vents extending from one side of a rib to theother side in the second direction, whereby flow channels are providedthrough the vents and the flow channels defined by the perforationslying between each adjacent pair of lands provide a flow passage tocross the plates in the second direction, wherein a deposit of catalyticmaterial is retained within the passageways of the said at least onegroup of plates.
 2. A heat exchanger or fluid mixing means comprising abonded stack of plates, the stack comprising at least one group ofplates, comprising one or more perforated plates (50) sandwiched betweena pair of primary separator plates, each perforated plate has aplurality of perforations arranged in rows across the plate in a firstdirection, with a land between each adjacent pair of perforations in arow and with ribs (54) between adjacent rows, the lands forming barriersto flow in the first direction across the plate and the ribs formingbarriers to flow in a second direction across the plate, the seconddirection being normal to the first direction, the ribs (54) havingvents (56) through a portion of their thickness, the vents (56)extending from one side of a rib (54) to the other side in the seconddirection, whereby flow channels are provided through the vents (56) andthe flow channels defined by the perforations lying between eachadjacent pair of lands provide a flow passage to cross the plates in thesecond direction, wherein the deposit of catalytic material is formed inthe perforations of the perforated plate(s).
 3. A heat exchanger orfluid mixing means according to claim 2, wherein the perforations of theperforated plates are elongate slots (52).
 4. A heat exchanger or fluidmixing means according to claim 3, wherein the vent has a base surfaceand the deposit is formed in the slots (52) to a level with said basesurface.
 5. A heat exchanger or fluid mixing means according to claim 2,characterised in that the vents (56) are formed on one surface of theirrib (54) to extend partially into the thickness of the rib (54).
 6. Aheat exchanger or fluid mixing means according to claim 5, wherein thevents (56) in adjacent pairs of ribs (54) are offset from each other. 7.A heat exchanger or fluid mixing means according to claim 6,characterised in that the vents (56) are formed normal to the directionof the rib (54).